Geologicheskii Vestnik

Paleobiological attribution of part of microfossils from a section of South Ural is suggested on the basis of the actuapaleontologic conclusions drawn in forms and their morphologic seriesfrom Precambrian section of the Baikal folded area and the Anabar-Olenek region. The short lithologic characteristic of Riphean type section lasting more than one billion years is provided. The age of series and formations is corrected according to the latest isotope chronological data. The history of studying of microfossils of Riphean stratotype is shown. Microfossil associations had been studied from the Zigazino-Komarov and Avzyan Formations of the Middle Riphean, and Zilmerdak,Inzer and Uk Formations of the Upper Riphean. Among new forms of the Avzyan Formation, Octaedryxium Rud. had been described, which was known earlier from the Late Riphean. Small volume-preserving forms are identified as benthos of chemolithotrophic or sulfur bacterias. Rich microfossil association of the Upper Riphean includes various cyanobacteria and acritarchs. Of the latter, a new species Trachyhystrichosphaera Tim. et Herm. is interesting, as well as forms, identified as desmidian green algae. Some forms are found which in the Neoproterozoic of the South of Eastern Siberia are included into association of the microfossils compared to coenobic green algae. Volumepreserving Retiforma Mikh. and Bavlinella faveolata Schep. were found, which were known earlier only from the Vendian. It is shown that the difference in the taxonomical content of the microbiotas is greatly influenced by a difference in sedimentation environments.

ultramafic rock, peridotite, dunite, chrome spinel, olivine, orthopyroxene, ophiolite, Kraka

• Arai S. Characterization of spinel peridotites by olivinespinel compositional relationships: Review and interpretation // Chemical Geology. 1994. V. 113. P. 191–204. doi.org/10.1016/0009-2541(94)90066-3.
• Chashchukhin I.S., Votyakov S.L., Shchapova Yu.V. Kristallokhimiya khromshpineli i oksi termobarometriya ultramafitov skladchatykh oblastey [Crystal chemistry of chrome spinel and oxithermobarometry of ultramafites of fold belts]. Yekaterinburg: IG&G UrB RAS, 2007. 310 p. (in Russian).
• Dick H.J., Bullen T. Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas // Contributions to Mineralogy and Petrology. 1984. V. 86. P. 54–76. doi.org/10.1007/bf00373711.
• Jacques, J.L., Green D.H. Anhydrous melting of peridotites at 0–15 kb pressure and the genesis of tholeiitic basalts // Contributions to Mineralogy and Petrology. 1980. V. 73. P. 287–310. doi.org/10.1007/bf00381447.
• Johnson C. Podiform chromite at Voskhod, Kazakhstan: Ph. D. thesis. Cardiff University, 2012. 468 p.
• Kelemen P.В., Shimizu N., Salters V.J.M. Extraction of mid-ocean-ridge basalt from the upwelling mantle by focused flow of melt in dunite channels // Nature. 1995. V. 375. P. 747–753. doi.org/10.1038/375747a0.
• Melcher F., Grum W., Simon G., Thalhammer T.V., Stumpfl E.F. Petrogenesis of the ophiolitic giant chromite deposits of Kempirsai, Kazakhstan: a study of solid and fluid inclusions in chromite // Journal of Petrology. 1997. V. 38. P. 1419–1458. doi.org/10.1093/petrology/38.10.1419.
• Pearce J., Barker P.F., Edwards S.J., Parkinson I.J., Leat P.T. Geochemistry and tectonic significance of peridotites from the South Sandwich arc-basin system, South Atlantic // Contribution to Mineralogy and Petrology. 2000. V. 139. P. 36–53. doi.org/10.1007/s004100050572.
• Rusin I.A. Granat-soderzhatchie associazii v giperbasitakh massiva Kraka (Yuzhny Ural) [Garnet-bearing assemblages in the gyperbasites of Kraka massif (the Southern Urals)] // Ezhegodnik–2001. Ekaterinburg:IGG UrB RAS, 2002. P. 134–137 (in Russian).
• Saveliev D.E., Belogub E.V., Blinov I.A., Kozhevnikov D.A., Kotlyarov V.A. Petrologicheskie svidetel’stva sindeformazionnoy segregazii vetchestva pri obrazovanii dunitov [Petrological evidences of syndeformation segregation of matter during a dunite formation (on the example Kraka ophiolites, the Southern Urals)] // Mineralogiya [Mineralogy]. 2016. V.4. P.56–77 (in Russian).
• Saveliev D.E., Puchkov V.N., Sergeev S.N., Musabirov I.I. Deformation-induced decomposition of enstatite in mantle peridotite and its role in partial melting and chromite ore formation // Doklady Earth Sciences. 2017. V. 476, No. 1. P. 1058–1061. DOI: 10.1134/S1028334X17090161.
• Saveliev D.E., Snachev V.I., Savelieva E.N., Bazhin E.A. Geologiya, petrogeokhimiya i khromitonosnost' gabbro-giperbazitovykh massivov Yuzhnogo Urala.[Geology, petrogeochemistry, and chromite content of gabbro-hyperbasic massifs of the South Urals]. Ufa: DizaynPoligrafServis, 2008. 320 p. (in Russian).
• Savelieva G.N. Gabbro-ultrabazitovyye kompleksy ofiolitov Urala i ikh analogi v sovremennoy okeanicheskoy kore [Gabbro-ultrabasitical complexes of the Urals ophiolites and their analogues in the present-day oceanic crust]. Moscow: Nauka, 1987. 230 p. (in Russian).
• Zhou M.F., Robinson P.T., Bai W.J. Formation of podiform chromites by melt/rock interaction in the upper mantle // Mineralium Deposita. 1994. V. 29. P. 98–101. doi.org/10.1007/bf03326400.